Precast Parking Garage Detailing: Double Tees, Spandrels & Structural Framing

Precast concrete parking structures represent one of the most technically demanding disciplines in structural detailing. From double tee framing grids to complex beam-tocolumn connections, every element must be coordinated with precision — integrating structural performance, drainage, expansion, and erection sequencing into a cohesive set of shop drawings and BIM models.

Precast Detailing Nov 13, 2026 0 32 Add to Reading List

Precast Parking Garage Detailing: Double Tees, Spandrels & Structural Framing

Understanding Precast Structural Systems & Framing Arrangements

The Precast System Logic

Precast parking garages rely on a fully integrated gravity and lateral system assembled from factory-fabricated components. The structural logic flows from columns up through beams and spandrels, then across double tee floor and roof members. Understanding how load paths interact at every connection is fundamental to producing accurate shop drawings and clash-free BIM models.

Lateral resistance is typically provided by shear walls, moment frames, or a combination — all of which must be coordinated with the diaphragm behavior of the double tee field.

Double Tee Floor & Roof Framing

Double tees (DTs) are the workhorse of precast parking framing. Standard widths range from 10 ft to 15 ft, with stem depths varying from 24" to 34" depending on span. Roof tees are typically lighter-gauge with shallower sections. Key detailing considerations include:

Bay spacing and bearing length on inverted tee beams or ledger beams (minimum 3" bearing is standard)

Flange-to-flange weld plates (standardized at PCI-recommended intervals) for diaphragm continuity

Camber allowances and differential camber between adjacent tees — critical for traffic surface smoothness

Topping slab coordination (topped vs. untopped systems) and their effect on connection design

Roof DT slope (typically 1.5% minimum) for positive drainage away from drain points

Framing Grid

DT bays are typically arranged on a 60 ft module with 30–34 ft spans. Grid coordination must account for ramp geometry, stair/elevator cores, and expansion joint locations.

Drainage Slopes

Floor drainage is achieved by sloping the supporting beams (not the tees themselves) or by varying DT seat elevations. A 1.5%–2% cross slope is standard across traffic aisles and stalls.

Spandrel & Interior Beams

Inverted tee (IT) beams carry DT stems at the interior bays. L-shaped ledger beams are used at ramps and special conditions. Beam depths must clear ramp headroom requirements.

Column Lines

Precast columns are typically 18"×18" to 24"×24" and are designed with corbels or hidden steel haunches to receive beam reactions. Column splice locations are carefully coordinated with erection equipment reach.

Precast Parking Structure Detailing

Spandrels, Columns, Wall Panels
& Connection Details

Spandrel beams, columns, wall panels, and their connections must transfer gravity, lateral, and torsional forces while accommodating volume-change movements from creep, shrinkage, and thermal effects. Precise detailing of bearing pads, grouted connections, weld plates, and embeds is essential to precast parking structure performance.

Structural & architectural

Spandrel Beams & Facade Panels

Spandrel beams serve a dual function: they are primary structural members carrying double tee reactions at the building perimeter, and they define the architectural facade of the structure. L-shaped spandrels are most common, with the horizontal leg providing the DT bearing seat and the vertical face forming the exterior. Detailers must resolve:

Torsional loading from eccentric DT reactions—spandrels must be tied back to the floor diaphragm with hairpin ties or strap angles to resist rotation.

Facade reveals, rustication, and architectural finishes—cast-in blockouts, reveals, and form liner textures must be precisely located in shop drawings.

Guardrail and bumper curb embeds—cast-in anchors for traffic barriers require careful placement relative to spandrel reinforcement.

Drainage weep holes—spandrels must include openings at the base to drain the floor slab level.

Most complex element

Beam-to-Column & Floor-to-Frame Connections

Connection design is the most critical—and most complex—element of precast parking detailing. Each connection must transfer gravity, lateral, and torsional forces while accommodating volume change movements from creep, shrinkage, and thermal effects.

Beam-to-column: Typically uses a welded bearing plate on a column corbel, with a bearing pad (elastomeric or PTFE) to allow rotation and translation. Positive moment connections at frame joints use mild steel dowels grouted into sleeves.

DT-to-beam: Stem pockets or welded clip angles receive the DT stem. Shim stacks and grout pad level variations accommodate camber and slope discrepancies.

Flange weld plates: Standardized PCI weld plates (3"×6" or similar) connect adjacent DT flanges and must be shown on erection drawings at prescribed spacing—typically 5 ft on center with closer spacing near shear walls.

Diaphragm chord steel: Continuous mild steel bars or strand spliced at DT ends tie the diaphragm perimeter and must be shown in both the structural design and the shop drawing set.

Connection hardware

Bearing Pads, Grout & Embedded Hardware

Bearing pads

Rotation & Translation

All beam-to-column and DT-to-beam bearing conditions require elastomeric or PTFE bearing pads. Pad dimensions, durometer, and allowable rotation must be coordinated with the structural engineer of record (EOR) and confirmed on shop drawings.

Grouted connections

Force Transfer

Dowel sleeves, shear keys, and column base plates rely on non-shrink grout for force transfer. Grout pockets must be detailed with adequate access for placement and consolidation, and grout strength must be specified to match design assumptions.

Weld plates & embeds

Tight-Tolerance Placement

All cast-in embeds—weld plates, insert plates, corbel anchor bars—must be located to tight tolerances. Shop drawings must cross-reference embed schedules with both the structural drawings and the erection sequence to avoid conflicts.

Parking structure detailing

Coordinate every spandrel, bearing, embed, and connection before fabrication.

Resolve torsion, facade detailing, drainage, bearing pads, grout pockets, and embed schedules across structural, shop, and erection drawings.

PRECAST PARKING STRUCTURES

Drainage Slopes, Floor Openings, Expansion Joints & Diaphragm Coordination

Beyond individual member detailing, the precast parking structure must function as a coordinated system — managing water, accommodating movement, and acting as an integrated structural diaphragm. These system-level details are where coordination errors are most costly.

SYSTEM MAP · SCHEMATIC PLAN VIEW

1 · Drainage slope 2 · Floor opening 3 · Expansion joint 4 · Diaphragm & shear wall

1 · DRAINAGE

typical max cross slope on accessible routes (ADA)

Drainage Slope Strategy

Floor drainage in precast structures is achieved by:

Sloping beam seats Varying DT flange elevations Sloped topping

Detailers must:

✓ Track finish floor elevations at every grid intersection

✓ Confirm cross slopes do not exceed code limits

✓ Coordinate drain inlet locations with the plumbing engineer

✓ Show spot elevations on erection drawings for field verification

2 · OPENINGS

opening types interrupt the DT framing grid

Floor Opening Coordination

Stair openings Elevator shafts Mechanical penetrations Sump locations

These require supplemental framing — typically steel headers or precast diaphragm segments.

Coordinate every opening with the BIM model to confirm that:

✓ DT stems are not cut

✓ Supplemental reinforcement is detailed

✓ Adjacent tee camber does not create slab level conflicts at the opening perimeter

3 · JOINTS

200–300 ft

typical expansion joint interval

2″–4″

common joint widths

Expansion Joints

Precast structures experience significant volume change from thermal, creep, and shrinkage effects. Joints break the structure into independent frames, and joint widths must accommodate calculated movements.

AT THE JOINT

Double columns or sleeved connections allow independent movement of adjacent frames

JOINT COVERS

Seal against water infiltration while allowing movement — traffic-rated compression seals or foam-filled covers

4 · DIAPHRAGM

EOR

diaphragm force diagram sets flange weld plate size and spacing

Diaphragm Connections

The double tee field acts as the horizontal diaphragm, distributing lateral forces to shear walls or moment frames.

DT field → Flange weld plates → Collectors → Spandrel connections → lateral system

Chord forces at diaphragm boundaries require continuous mild steel or strand.

Collector elements at shear wall ends must be fully detailed, including the transfer of collector forces through spandrel connections back into the lateral system.

WHY IT MATTERS

Water, movement, and lateral load all cross member boundaries — which is why these system-level details are where coordination errors are most costly.

Erection Drawings, BIM Coordination & Structural Shop Drawing Best Practices

What Erection Drawings Must Communicate

Erection drawings are the field-facing documents that guide the precast installer from first piece to final closure. A complete, well-organized erection drawing set for a parking structure includes:

**Piece mark plans:** Every column, beam, spandrel, DT, and wall panel assigned a unique mark tied to the piece schedule

**Erection sequence notes:** Order of piece installation, temporary bracing requirements, and hold points for field welding or grouting

**Bearing and seat elevations:** Tabulated at each support point, accounting for camber, drainage slope, and topping thickness

**Connection details:** Referenced from detail sheets — weld plate types, shim requirements, grout pocket dimensions, and field weld symbols

**Embed schedules:** Cast-in anchors, insert plates, and hardware cross-referenced to both shop and erection drawings

**Tolerances:** PCI MNL-135 erection tolerances noted for critical dimensions — particularly column plumb, beam seat elevation, and DT bearing

BIM Modeling for Precast Parking Structures

BIM modeling has become standard practice for complex precast structures. A well-executed precast BIM model for a parking garage provides:

Clash detection

Automated checking for DT stem vs. beam flange conflicts, embed vs. rebar interference, and mechanical vs. structural penetration conflicts

Quantity extraction

Accurate piece counts and concrete volumes for estimating and procurement

Erection visualization

4D sequencing models that allow the erection contractor to plan crane picks and staging before mobilization

Drawing automation

Parametric models in Revit or Tekla Structures can generate piece drawings, elevation views, and schedules directly from the model, reducing manual drafting errors

Coordination with MEP

Linked models allow early identification of conflicts between precast structure and mechanical, electrical, and plumbing systems

PCI MNL-135 (Tolerance Manual for Precast and Prestressed Concrete) and ACI 117 set the governing dimensional tolerances that must be reflected in both shop drawings and BIM model clearances.

Structural Shop Drawing Workflow

Structural Design Coordination

Obtain EOR-issued design drawings, connection force tables, diaphragm force diagrams, and volume change calculations before beginning shop drawing production. Resolve all RFIs before detailing begins.

BIM Model Development

Build the parametric 3D model from column bases up — columns, beams, spandrels, then DTs. Assign piece marks, embed locations, and connection hardware in the model before extracting drawings.

Shop & Erection Drawing Production

Generate piece drawings, embed schedules, erection plans, and connection details. Cross-reference all documents and confirm that bearing elevations, slope strategies, and expansion joint details are consistent across all sheets.

EOR & Contractor Review

Submit for EOR review and contractor coordination. Address all comments, confirm erection sequence with the installer, and re-issue for construction. Field RFIs during erection should be tracked and resolved with formal sketch supplements.